This invention relates to the field of ultrasonic drilling, and, more specifically, to ultrasonic drilling apparatus providing a continuous slurry feed through a hollow drill bit to flush the bit throughout a drilling operation. The invention is a result of a Contract with the Department of Energy (Contract No. W-7405-ENG-36).
Ultrasonic drilling is a highly developed art used to machine or drill difficult materials such as ceramics, glasses, and refractories, as well as very hard materials such as high purity (purity higher than 98%) boron carbide, kyon, silicon carbide, tantalum carbide and the like. In ultrasonic drilling, the drill bit reciprocates at an ultrasonic frequency of approximately 20 kilohertz and an amplitude of approximately 0.0008 in., and, if not an impact machine, also rotates. In some applications, a drilling slurry containing abrasive particles is flowed about the drill bit during the drilling process.
For the drilling of very hard materials, tubular drill bits with diamond cutting edges and an abrasive slurry are used. However, it has been heretofore impractical to drill a hole deeper than about three-eighths of an inch in materials whose hardness approaches that of diamond. This is particularly true with high purity boron carbide, which is about 14.7 on the revised Moh scale. Deeper drilling is prevented by the action of the abrasive particles and workpiece cuttings adhering to or wiping the diamond edge of the bit, rendering it ineffective.
As stated, a diamond edged ultrasonic bit with an abrasive slurry can drill into a material such as high purity boron carbide a distance of only approximately three-eighths of an inch. Beyond this distance, conventional methods of supplying slurry to the bit are not effective in keeping the bit clean. To drill deeper holes, it is necessary to maintain a flow of slurry across the edge of the drill bit, while still providing effective ultrasonic reciprocation.
One attempt at solving this problem in an impact only machine is disclosed in U.S. Pat. No. 3,091,060 to Giegerich et al. In one embodiment slurry is introduced around the bit and withdrawn through a passage in the machine member. Another embodiment has the slurry being introduced around the bit and withdrawn through a pilot hole in the material being drilled. However, it is very doubtful that simply pouring slurry at the surface of the workpiece would be effective to deliver slurry to the tip of the bit when the tip has drilled beyond a short distance from the surface of the workpiece. While the method disclosed in this patent may be effective for impact machines drilling shallow holes, it teaches nothing about obtaining a flow of slurry in a rotating ultrasonic drill. Impact machines, even with slurry flow, cannot satisfactorily drill high purity boron carbide.
It is therefore an object of the present invention to provide an apparatus for rapidly drilling deep holes in hard materials such as boron carbide.
It is another oject of the present invention to rapidly drill holes in very hard materials without undue mechanical or thermal stresses to the material.
It is another object of the present invention to provide apparatus for drilling deep holes in hard materials which may be easily mounted on existing ultrasonic drills.
An advantage of the present invention is that apparatus in accordance with the invention requires little downtime for bit cleaning and other maintenance.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.